One of those annoying questions that should be simple, but that I've forgotten how to do:
Two lines are given by the equations r1=a+lp and r2=b+mq. Find the condition for the lines to cross, and find there position of intersection.
The Attempt at a Solution
I've done the first bit: (a-b).(p*q)=0 where * means the cross product. But I can't find a way of doing the second bit (find the point of intersection), I'd know how to do it if the actual vectors were given, but how do you write in in a nice vector form?